The goal of this proposal is to isolate and characterize the different apolipoprotein and lipoprotein forms of lipoprotein D (LP-D) and to clarify the relationship between LP-D and lecithin:cholesterol acyltransferase (LCAT). It is hypothesized that LP-D is the substrate-product carrier of LCAT action and LP-D is involved in the redistribution of cholesterol/cholesterol esters between various lipoprotein species and/or peripheral membranes. The specific aims of the proposed research are 1) isolate and characterize the multiple forms of ApoD, 2) isolate and characterize the multiple forms of LP-D, 3) isolate and prepare antiserum to purified LCAT, and 4) examine the structural and metabolic relationship between LP-D and LCAT. The studies outlined in this proposal should establish whether LP-D is required for esterification of cholesterol and/or the flux of cholesterol between various lipoprotein species and/or peripheral membranes. Since elevated plasma cholesterol levels are a known risk factor in the development of atherosclerosis, additional information regarding the details of cholesterol transport in plasma may be of use in understanding some of the processes in the deposition of cholesterol in peripheral membranes.